saravananlinux

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For more information about the High Availability Add-On and the Resilient Storage Add-On for Red Hat Enterprise Linux 6, refer to the following resources: High Availability Add-On Overview — Provides a high-level overview of the Red Hat High Availability Add-On. Cluster Administration — Provides information about installing, configuring and managing the High Availability Add-On. DM Multipath — Provides information about using the Device-Mapper Multipath feature of Red Hat Enterprise Linux. Load Balancer Administration — Provides information on configuring high-performance systems and services with the Load Balancer Add-On, a set of integrated software components that provide Linux Virtual Servers (LVS) for balancing IP load across a set of real servers.

Tried various possibilities to configure the secondary MX server to queue mails properly if primary MX fails. Today tried the secondary MX setup with below configuration and it worked out.....   In main.cf file,   relay_domains = $mydestination example.com smtpd_recipient_restrictions = permit_mynetworks check_relay_domains   Included the transport_maps too in main.cf file in which configured the domain smtp transport address: transport_maps = hash:/etc/postfix/transport   In /etc/postfix/transport file,   example.com smtp:mail.example.com     Concept:-   If primary mail server for the domain example.com will down then all the mails are backuped/queued in secondary/backup mail server[postfix] once the primary server will be ready then mails are delivered  from backup to primary server.

Refer:- http://docs.cloudstack.apache.org/en/master/concepts.html#what-is-apache-cloudstack What is Apache CloudStack? Apache CloudStack is an open source Infrastructure-as-a-Service platform that manages and orchestrates pools of storage, network, and computer resources to build a public or private IaaS compute cloud. With CloudStack you can: Set up an on-demand elastic cloud computing service. Allow end-users to provision resources Cloud Infrastructure Overview Resources within the cloud are managed as follows: Regions: A collection of one or more geographically proximate zones managed by one or more management servers. Zones: Typically, a zone is equivalent to a single datacenter. A zone consists of one or more pods and secondary storage. Pods: A pod is usually a rack, or row of racks that includes a layer-2 switch and one or more clusters. Clusters: A cluster consists of one or more homogenous hosts and primary storage. Host: A single compute node within a cl...

Emulated devices Emulated devices, sometimes referred to as virtual devices, exist entirely in software. Emulated device drivers are a translation layer between the operating system running on the host (which manages the source device) and the operating systems running on the guests. T he device level instructions directed to and from the emulated device are intercepted and translated by the hypervisor. Any device of the same type as that being emulated and recognized by the Linux kernel is able to be used as the backing source device for the emulated drivers.  Para-virtualized Devices Para-virtualized devices require the installation of device drivers on the guest operating system providing it with an interface to communicate with the hypervisor on the host machine. T his interface is used to allow traditionally intensive tasks such as disk I/O to be performed outside of the virtualized environment. Lowering the overhead inherent in virtualization in this manner is intended to a...

A VLAN (Virtual LAN) is an attribute that can be applied to network packets. Network packets can be "tagged" into a numbered VLAN. A VLAN is a security feature used to completely isolate network traffic at the switch level. VLANs are completely separate and mutually exclusive. T he Red Hat Enterprise Virtualization Manager is VLAN aware and able to tag and redirect VLAN traffic, however VLAN implementation requires a switch that supports VLANs. At the switch level, ports are assigned a VLAN designation. A switch applies a VLAN tag to traffic originating from a particular port, marking the traffic as part of a VLAN, and ensures that responses carry the same VLAN tag. A VLAN can extend across multiple switches. VLAN tagged network traffic on a switch is completely undetectable except by machines connected to a port designated with the correct VLAN. A given port can be tagged into multiple VLANs, which allows traffic from multiple VLANs to be sent to a single port, to be deci...

QCOW2 Formatted Virtual Machine Storage QCOW2 is a storage format for virtual machine disk images. QCOW stands for QEMU copy on write. T he QCOW2 format decouples the physical storage layer from the virtual layer by adding  a mapping between logical and physical blocks. Each logical block is mapped to its physical offset, which enables storage over-comittment and virtual machine snapshots, where each QCOW volume only represents changes made to an underlying disk image. T he initial mapping points all logical blocks to the offsets in the backing file or volume. When a virtual machine writes data to a QCOW2 volume after a snapshot, the relevant block is read from the backing volume, modified with the new information and written into a new snapshot QCOW2 volume. T hen the map is updated to point to the new place. RAW T he RAW storage format has a performance advantage over QCOW2 in that no formatting is applied to virtual machine disk images stored in the RAW format. Virtual machi...